When You are in creative mode and you are flying, you will go the normal speed for flying but if you stay still for about 5 seconds and then start moving again, you will be slow as if you were on the ground and walking. if you fly up a little than it goes the correct speed but it is super annoying in pocket edition and sort of annoying in xbox one edition.
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Thank you for your report!
However, this issue is a Duplicate of MCPE-32391.
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